Re: [loopantennas] Re: loop antenna - has to be in resonance?
> ... This is true for all RF circuits - as long as you have a lowWell, no, that is not true.
> impedance driving a high impedance, you will have little or no reflection,
> low SWR, and matching is not required.
If there is some amount of transmission line (coax, feedline, etc.),
and if it is a low impedance line driving a high impedance load, then
you WILL get reflection, and high SWR.
But if the line lengths are short and the frequencies low enough so
that the length is electrically short, then you can treat it as a low
frequency circuit, and then the SWR that is on that short line may not
bother you. Then, you can get maximum voltage at the load by
connecting a high impedance load to the low impedance source. But you
still do not get maximum power transfer except when the impedances
For reception of radio signals sent short distances, impedance
mismatches (and consequent reception inefficiency) is OK because your
received signals are so strong.
When the received signals are weaker, like they usually are in radio
communications, it's a different story. We can often tolerate the
mismatch+inefficiency on MF and HF because the atmospheric noise tends
to dominate the signal-to-noise and everything is greater than the
receiver's own noise, so some loss in received power (due to the
mismatch) doesn't hurt the S/N ratio. But once you get up into VHF
and above, you really need to match impedances between antenna and
receiver because the receiver's noise is the limiting factor. A
mismatch between the antenna and receiver causes signal loss and
degraded S/N, and likely inability to receive weaker signals that you
should have been able to receive.
> Add a fixed resistor in series with the parallel RCI am guessing you meant to write inductor or capacitor, not resistor.